This invention relates to improvements in carbon to carbon friction clutches.
These mechanisms employ carbon disks for both the driver and the driven plates; the disks are free standing, i.e. the carbon is not applied as a facing material for steel disks. Carbon in this application has two major advantages: its coefficient of friction increases with temperature--a desirable property when the clutch is engaged and disengaged repeatedly in short periods of time; it has a density which is half of that of steel--light weight clutches can easily be designed with the use of carbon.
Carbon also has two disadvantages: it has a relatively low compressional strength and it abrades easily. In recent years methods have been devised for improving carbon's physical properties. In one process (Watts et al., U.S. Pat. No. 3,932,568) carbon particles are heated, mixed with phenolic resin and molded into plates under heat and pressure. Another process (Nitz, U.S. Pat. No. 3,552,533) involves the adding of carbon reinforcing fibers to a carbon matrix and hot pressing the latter in a mold. These and other processes have made it possible to design a clutch which uses free standing disks of carbon. This kind of unit is described by Marin, U.S. Pat. No. 3,759,353. A carbon to carbon clutch of this type will operate satisfactorily at low and moderate loads. A carbon driven plate which depends on carbon teeth to mesh with steel splines in an output shaft would fail in shear as the load became high, even with the improved carbon material. In racing cars loads are very high as the driver accelerates and decelerates during various maneuvers. A carbon to carbon clutch made in accordance with the prior art would therefore have a limited life.
If a suitable means were available for reinforcing the driven plates against compressional failure, the second disadvantage--high abrasion rate can also be minimized. The driving and driven plates can be arranged so that they "float" during clutch disengagement. This allows both sets of plates to "rearrange" themselves axially prior to each re-engagement, a situation which minimizes abrasive wear. It is also possible in a carbon to carbon clutch to use less steel in the overall construction, substituting lighter metals, with the net result of increased maneuverability during racing.
It is one objective of the present invention to reinforce the driven carbon plate so that it can withstand high compression loading.
It is a second objective to incorporate an axial "floating" action in the clutch so that a uniform and low wear rate is achieved and the effects of initial axial misalignment are minimized.
According to the present invention the driver and driven plates are mounted between a clutch cover and the flywheel of the car's engine. Separation between cover and flywheel is maintained by a series of radially distributed blocks bolted between them. The driver plates contain apertures on their outer peripheries to accommodate the blocks; the driver plates thus have axial freedom when the clutch is disengaged because they can slide axially along these blocks. The driven plates contain a central hole with slots formed at even intervals around the periphery of the hole. A splined, light-metal hub containing fingers which fit the slots serves to couple the driven plates to the output shaft. The number of slots in the carbon driven plates can be chosen to vary the area of contact with the hub and thus control the compressional load. The driven plates can "float" when the clutch is disengaged on the hub fingers and as a result of the hub's movement on the spline.
Another feature of the present invention is the reduction of the temperature gradient between the driven carbon disk and the output shaft. The metal hub serves as a heat sink between the carbon and the steel output shaft. Expansion differences between the carbon of the driven plates and the metal of the hub fingers and however not important because of the non-rigid attachment.
One embodiment of the invention will be described to illustrate the general principles with respect to the following drawings.